Table support in RCSS is similar to that of the CSS tables specifiation. There are some enhancements and differences, the main ones being as follows.

  • The width of columns and height of rows support flexible sizing (like using the CSS fr unit for grid layout).
  • Minimum and maximum size constraints are respected for column widths and row heights.
  • Spacing between rows and between columns can be controlled individually using margin, border and padding.
  • The width of columns are computed as if setting the CSS property table-layout: fixed, with the above enhancements.
  • RmlUi does not generate anonymous elements or attempt to clean up invalid tables.
    • Table row elements must be present for borders to be generated as specified for the row.
    • Table cells will not inherit any properties from the column elements they belong to, except for adjusting the width.
  • Percentage-relative values are calculated based on the initial block-size of the table element, and are not re-adjusted if the table size is changed during formatting.

The RCSS table model

The RCSS table model follows the structure of CSS tables. This means that the table is made up of table rows, optionally wrapped in row groups, which contain individual cells. Table columns and column groups can optionally be specified for visual effects (mainly backgrounds, borders, and decorators) and for defining widths of columns. Columns never contain cells directly. Table columns and column groups must precede any rows or row groups. Table cells can be placed as direct children of the table, then consecutive cells will form a new row.

The display property is used to define the formatting of tables, with the following relevant values.

display value Description Attributes Valid children
table Specifies a block-level table.   table-row, table-row-group,
table-column, table-column-group,
table-row Specifies a table row.   table-cell
table-row-group Specifies a grouping of table rows.   table-row
table-column Specifies a table column. span  
table-column-group Specifies a grouping of table columns. span (when no children present) table-column
table-cell Specifies a table cell. colspan, rowspan  

In particular, the following CSS display modes are not supported: inline-table, table-header-group, table-footer-group, table-caption.


The following example demonstrates a table with grouped rows and columns, using all the table display modes.

		<col span="2"/>
			<td colspan="2">Items</td>
			<td>139 years</td>
			<td colspan="4">Footnote</td>

This example assumes that the recommended stylesheet below is applied.

Unlike in HTML, the table element or any of the other table tags do not have any special meaning in RmlUi. Instead, they will be derived entirely from their RCSS properties. Furthermore, RmlUi does not contain a default stylesheet, thus, the RCSS properties for tables must first be declared. The following RCSS properties are recommended for declaring tables with the tags known from HTML.

table {
	box-sizing: border-box;
	display: table;
tr {
	box-sizing: border-box;
	display: table-row;
td {
	box-sizing: border-box;
	display: table-cell;
col {
	box-sizing: border-box;
	display: table-column;
colgroup {
	display: table-column-group;
thead, tbody, tfoot {
	display: table-row-group;

Visual layout of tables

Table elements are rendered in the following order, from bottom to top:

  1. Table
  2. Column groups
  3. Columns
  4. Row groups
  5. Rows
  6. Cells

Column groups and column elements are sized to cover the table columns they are spanning. Row groups are sized to cover the rows they are spanning. This way, backgrounds, borders, and decorators can be used on these elements, and will be visible if cells and rows have transparent backgrounds.

Table width algorithm

The table width is the sum of all table columns and the horizontal table spacing, such as column-gap, column margins, and table padding.

The width of table columns are defined entirely by the width specified on column elements and/or the cells of the first row. In the following, columns mean any of the aforementioned elements.

  • Columns with width: auto are distributed equally to fill the table width.
  • Columns with width: <length> | <percentage < 100%> will use the specified value.
  • Columns with width: <percentage ≥ 100%> adjusts the flexible width of the column relative to other flexible columns (like the CSS fr unit for grid layout).
  • Columns can specify min-width and max-width to constraint their sizing.

Unlike in CSS, column groups and columns can use horizontal padding, border and margin. This will be added to the horizontal spacing of the table. Column groups and columns can also use vertical border and margin to add borders and offset them from the table edges, but will not affect the position of the cells.

Table height algorithm

The table height is determined by the sum of the height of all its rows, in addition to vertical spacing such as row-gap, row margins, and table padding.

Each row has their height determined as follows:

  • Rows with height: auto determine their height by the tallest formatted cell in the row.
  • Rows with height: <length> | <percentage < 100%> will use the specified value.
  • Rows with height: <percentage ≥ 100%> adjusts the flexible height of the row relative to other flexible rows (like the CSS fr unit for grid layout).
  • Rows can specify min-height and max-height to constraint their sizing.

If the rows do not fill the height specified on the table, all rows will be scaled up proportionally while respecting any max-height constraints. If there is still space available, empty space will be left at the bottom of the table.

All percentage values are resolved using the initial block height of the table. Thus, if the table height is specified as auto, they will resolve to zero. Instead, the table height should be set to a specific length. Percentage heights can also be used if the parent element’s height is specified.

Unlike in CSS, row groups and rows can use vertical padding, border and margin. This will be added to the vertical spacing of the table. Row groups and rows can also use horizontal border and margin to add borders and offset them from the table edges, but will not affect the position of the cells.


When used on a table cell, this property has the following meaning.

top (default)
Aligns the table cell with the top of the first row it spans.
Aligns the table cell with the bottom of the last row it spans.
Aligns the table cell with the middle of the rows it spans.
Other values have no meaning in this context and defaults to top.

The alignment is done by adding top or bottom padding to the cell element. Unlike in CSS, baseline is currently not supported.


The model for setting borders on tables in RCSS is similar to the separated borders model in CSS (border-collapse: separate).

That is, each cell element control their own borders separately.

However, unlike CSS, borders can still be added to rows, row groups, columns, and column groups. They will be separated from the cell borders, as if extending the borders of their inner elements.

Cell spacing

row-gap, column-gap

Value: <length> | <percentage>
Initial: 0px
Applies to: table elements
Inherited: no
Percentages: relative to the height and width, respectively, of the initial table block size

Specifies the gap between table cells. Like the CSS property border-spacing, except that spacing is not applied before and after the first and last cell, respectively. Instead, use padding on the table element to add spacing between the table border and its cells.


A shorthand property for setting both row-gap and column-gap properties, in that order. If only a single value is specified, it sets both gap properties to the given value.